6.6 The Volume of a Mole of 6.6 The Volume of a Mole of a Gasa Gas

One-mole amounts of different solid One-mole amounts of different solid and liquid substances have different and liquid substances have different volumes.volumes. Example: Figure 6-7 – a mole of table sugar Example: Figure 6-7 – a mole of table sugar

has a larger volume of a mole of water.has a larger volume of a mole of water. The The volume of a gasvolume of a gas changes with changes with

temperaturetemperature and and pressurepressure.. Because of this, the Because of this, the volumes of gasesvolumes of gases are are

usually measures at usually measures at standard standard temperature and pressuretemperature and pressure (STP) (STP)

6.6 The Volume of a Mole of 6.6 The Volume of a Mole of a Gasa Gas

Standard Temperature and Pressure Standard Temperature and Pressure (STP)(STP) Standard temperatureStandard temperature is is 0°C0°C Standard pressureStandard pressure is is 101.3 kPa or 1 atm101.3 kPa or 1 atm

At STP, 1 mol of any gas occupies a At STP, 1 mol of any gas occupies a volume of 22.4 L.volume of 22.4 L. This quantity is referred to as the This quantity is referred to as the molar molar

volumevolume of a gas and is measured at STP. of a gas and is measured at STP. 22.4 L of any gas at STP is 1 mole of that 22.4 L of any gas at STP is 1 mole of that

gas, so it contains 6.02 x 10gas, so it contains 6.02 x 102323 representative representative particles of that gasparticles of that gas

6.6 The Volume of a Mole of 6.6 The Volume of a Mole of a Gasa Gas

Would 22.4 L of one gas have the Would 22.4 L of one gas have the same same mass mass as 22.4 L of another gas as 22.4 L of another gas at STP? Why or why not?at STP? Why or why not?

Hint: Image the two gases were Hint: Image the two gases were hydrogen (Hhydrogen (H22) and oxygen (O) and oxygen (O22).).

6.6 Example 8 – Moles to 6.6 Example 8 – Moles to VolumeVolume

Determine the volume, in liters, of Determine the volume, in liters, of 0.600 mol sulfur dioxide, SO0.600 mol sulfur dioxide, SO22, gas at , gas at STP.STP.

Unknown: Volume (L of SOUnknown: Volume (L of SO22))

Known: 0.600 mol SOKnown: 0.600 mol SO22

1 mol SO1 mol SO22 = 22.4 L of SO = 22.4 L of SO22 at STP at STP

Solution:Solution:0.600 mol SO0.600 mol SO22

11xx 22.4 L SO22.4 L SO22

1.00 mol SO1.00 mol SO22

== 13.4 L SO13.4 L SO22

6.6 Example 9 – Volume 6.6 Example 9 – Volume to Molesto Moles

Determine the number of moles in Determine the number of moles in 33.6 L of He gas at STP.33.6 L of He gas at STP.

Unknown: mol HeUnknown: mol He

Known: 33.6 L of HeKnown: 33.6 L of He

1.00 mol He = 22.4 L of He1.00 mol He = 22.4 L of He

Solution:Solution:

33.6 L He33.6 L He 11

xx1.00 mol He1.00 mol He 22.4 L He22.4 L He

==1.50 mol He1.50 mol He

6.7 Gas Density and the 6.7 Gas Density and the gmmgmm

The density of a gas is usually The density of a gas is usually measured in the units g/L.measured in the units g/L.

The experimentally determined density The experimentally determined density of a gas at STP is used to calculate the of a gas at STP is used to calculate the gram formula mass of that gasgram formula mass of that gas density = mass/volumedensity = mass/volume density = molar mass/molar volumedensity = molar mass/molar volume For gases at STP, density = molar For gases at STP, density = molar

mass/22.4 Lmass/22.4 L

6.7 Example 106.7 Example 10

The density of a gaseous compound The density of a gaseous compound of carbon and oxygen is 1.964 g/L at of carbon and oxygen is 1.964 g/L at STP. Determine its gram formula STP. Determine its gram formula mass. Is the compound COmass. Is the compound CO22 or CO? or CO?

Unknown: gfm (g)Unknown: gfm (g)

Known: 1.964 g/L; 1.964 g = 1 LKnown: 1.964 g/L; 1.964 g = 1 L

Solution:Solution:22.4 L22.4 L 11

xx1.964 g1.964 g 1 L1 L

== 44.0 g44.0 g

6.7 Example 106.7 Example 10

Is the compound COIs the compound CO22 or CO? or CO?gfm CO:gfm CO:12 g/mol (C) + 16 g/mol (O) = 28 g/mol12 g/mol (C) + 16 g/mol (O) = 28 g/mol

gfm COgfm CO22::12 g/mol (C) + 2(16 g/mol) (O) = 44 12 g/mol (C) + 2(16 g/mol) (O) = 44

g/molg/mol

Answer: The gas is COAnswer: The gas is CO22